The present invention is directed to measuring geometrical dimensions of a part and, more particularly, to a method and apparatus for measuring the diameter of a part, such as a ring.
Measuring the diameter of a ring has become an important step in the manufacture of a bearing. A number of known mechanical measurement techniques exist for measuring the diameter of a part. The mechanical measuring techniques commonly include the use of air gauges, calipers, micrometers, and pi tapes, to name a few. The pi tape measurement approach uses a measuring tape that includes the .pi. function included with the dimensional units in inches or centimeters, such that the circumferential measurement units are divided by the well-known ratio of circumference of a circle to its diameter, e.g., .pi.=3.14159265. As the pi tape is physically wrapped around the measured circumferential surface of the part, the measurement units provide an actual part measurement converted on the tape to a diameter unit. The caliper and micrometer measurement techniques likewise include mechanical methods of taking actual physical measurements to measure the diameter of the part.
In lieu of the mechanical techniques, a more recent approach called a coordinate measuring machine has been developed and used to establish coordinates for a given part surface. The coordinate measuring machine uses an algorithm to approximate the diameter of the part. This is generally accomplished by way of a "best fit" approach in which the circumference of the part is approximated and matched up with a best fit circle. However, the coordinate measuring machine only provides an approximate dimension and can be adversely affected by a non-round shape of the part, as well as various features that may be present on the measured part.
Accordingly, there is a need to provide for an accurate measuring apparatus to measure the diameter of a part quickly and with high reliability. Further, there is a need to provide for such a measuring apparatus and method that can achieve accurate measurements of parts that are out of round, and particularly for a ring shaped part.